1. Field of the Invention
The present invention relates to a real image finder of a camera.
2. Background Arts
A real image finder is usually composed of an objective lens, a field lens, an erect image optical system and an eyepiece. For example, Japanese Patent No. 2538525 discloses a zoom finder that is composed of an objective lens system consisting of a concave lens and a convex lens, a field lens, an erect image prism and an eyepiece, arranged in this order from the object side. Japanese Laid-open Patent application No. 7-159865 discloses a zoom finder that is composed of an objective lens system consisting of a concave lens and a convex lens, a prism integrally formed with a convex lens, an erect image prism and an eyepiece, arranged in this order from the object side. Japanese Laid-open Patent application No. 4-19705 discloses three embodiments of fixed magnification finders. The first embodiment is composed of an objective lens, a prism with a first reflection surface, and a prism with second to fourth reflection surfaces that functions as an eyepiece, which are arranged in this order from the object side. The second embodiment is composed of an objective lens, a prism with first and second reflection surfaces, and a prism with third and fourth reflection surfaces that functions as an eyepiece, which are arranged in this order from the object side. The third embodiment uses a reflection mirror in addition to an objective lens and two prisms.
As seen from the above examples, conventional real image type finders need at least four elements to be a zooming finder, or at least three elements for a fixed magnification. As the number of elements increases, the manufacturing cost of the finder increases. As the number of elements' surfaces and air gaps increases with the number of elements, the formed image gets dark because of the surface reflection.